How Did Lake Eyre’s Salt Crust Form? The Science Behind the White
Standing on the salt at Lake Eyre, it’s hard not to wonder about it. Where did all this salt come from? How thick is it? What’s underneath? The answers are more interesting than most people expect.
Where the Salt Comes From
The salt at Lake Eyre isn’t deposited from one source — it’s accumulated over millions of years through the geological process of evaporite deposition. When water flows into a closed basin (one with no outlet to the ocean), it brings dissolved minerals with it. As that water evaporates in the heat of the desert, the minerals are left behind. Repeat this process over a very long time and you get a very large accumulation of salt.
Lake Eyre sits at the bottom of the largest internally draining basin in Australia — the Lake Eyre Basin, covering about 1.14 million square kilometres. Every rain event across this vast catchment, every river that runs and evaporates, contributes minerals to the lake. Sodium chloride — common salt — is the most abundant result, which is why the lake’s surface is mostly white.
How Thick Is the Salt?
The salt crust varies in thickness across the lake. In some areas it’s just a centimetre or two — enough to walk on and hear crunch underfoot, but not much more. In other areas, particularly toward the centre of the lake and in areas that have been dry for longer periods without flooding to dissolve and redistribute the salt, the crust can be significantly thicker.
Beneath the salt crust is wet mud — the ancient lakebed clay that the salt sits on top of. When the crust is thin, you can break through it with a foot and find the mud beneath. This is one of the reasons access to the centre of the lake is restricted.
The Pink Colour — What Causes It
In certain areas and conditions, Lake Eyre’s surface isn’t white at all — it’s pale pink or even a deeper rose colour. This is caused by halobacteria: salt-tolerant microorganisms that produce a pink-red pigment as a byproduct of their metabolic processes. These bacteria thrive in the highly saline conditions of the lake’s brine pools and can colour large areas of the surface when conditions are right.
From the air in the scenic flight, the colour variation across the lake surface is one of the things that most surprises people — they expect white and get a landscape that shifts between white, cream, pink, grey, and pale blue depending on salinity, moisture, and where you’re looking.
What Flooding Does to the Salt
When Lake Eyre floods, fresh water diluting the highly concentrated salt brine creates interesting chemistry. The salt at the surface partially dissolves and redistributes. Minerals that were concentrated at the surface move into the water column. This is part of why flood events are ecologically productive — the sudden availability of dissolved minerals and the reduction in salinity to survivable levels for fish and invertebrates creates a brief but extraordinary burst of life.
When the flood recedes and the water evaporates again, new salt crystallises out of the water and the crust reforms. Each flood and drought cycle adds and reshapes the surface. The salt you’re crunching underfoot on a visit to the dry lake is the record of many such cycles.
What to Look for When You’re There
Up close, the salt surface is more varied than it looks from a distance. The polygon patterns — hexagonal shapes formed by the expansion and contraction of the salt crust as it wets and dries — are visible underfoot and beautiful in the right light. The edges of the polygons are raised slightly, creating a subtle texture across the surface that a morning or evening sun catches dramatically.
It’s one of the things that rewards slowing down when you get there, rather than just taking a photo from the edge and moving on.
